Add annotations in parameters for exports (#20140)

Closes #20127

Author: smarter

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1255,6 +1255,8 @@ class Namer { typer: Typer =>
               newSymbol(cls, forwarderName, mbrFlags, mbrInfo, coord = span)
 
           forwarder.info = avoidPrivateLeaks(forwarder)
+
+          // Add annotations at the member level
           forwarder.addAnnotations(sym.annotations.filterConserve { annot =>
             annot.symbol != defn.BodyAnnot
             && annot.symbol != defn.TailrecAnnot
@@ -1290,6 +1292,15 @@ class Namer { typer: Typer =>
               foreachDefaultGetterOf(sym.asTerm,
                 getter => addForwarder(
                   getter.name.asTermName, getter.asSeenFrom(path.tpe), span))
+
+            // adding annotations at the parameter level
+            // TODO: This probably needs to be filtered to avoid adding some annotation
+            // such as MacroAnnotations
+            if sym.is(Method) then
+              for (orig, forwarded) <- sym.paramSymss.lazyZip(forwarder.paramSymss)
+                  (origParameter, exportedParameter) <- orig.lazyZip(forwarded)
+              do
+                exportedParameter.addAnnotations(origParameter.annotations)
       end addForwarder
 
       def addForwardersNamed(name: TermName, alias: TermName, span: Span): Unit =

tests/neg/i20127.check

@@ -0,0 +1,8 @@
+-- [E172] Type Error: tests/neg/i20127.scala:13:9 ----------------------------------------------------------------------
+13 |  Foo.foo        // error
+   |         ^
+   |         foo!
+-- [E172] Type Error: tests/neg/i20127.scala:14:14 ---------------------------------------------------------------------
+14 |  FooClone.foo   // error
+   |              ^
+   |              foo!

tests/neg/i20127.scala

@@ -0,0 +1,14 @@
+import scala.annotation.*
+
+trait X
+
+object Foo:
+  def foo(using @implicitNotFound("foo!") x: X) = "foo"
+
+object FooClone:
+  export Foo.foo
+
+object Main:
+  val n = 10
+  Foo.foo        // error
+  FooClone.foo   // error